diff --git a/exam_template/python/Graph.py b/exam_template/python/Graph.py
index 4f9647c..341c70a 100644
--- a/exam_template/python/Graph.py
+++ b/exam_template/python/Graph.py
@@ -2,7 +2,7 @@ from sys import argv
 from pathlib import Path
 from math import sin, cos, pi
 
-from common import printc, replaceContent
+from common import printc, printerr, replaceContent
 
 class Matrix:
   """ Adjacency matrix which supports 0 and 1 """
@@ -127,6 +127,10 @@ class Graph:
     edges = []
     connected_subgraphs = [set(v) for v in self.nodes]
 
+    if not all(n in ''.join(x+y for x,y in self.edges) for n in self.nodes):
+      printerr('Not all nodes are connected. There is no spanning tree to be made')
+      return
+
     def find_subgraph_containing(v):
       return [x for x in connected_subgraphs if v in x][0]